This invention relates to hand controls and, in particular, to hand controls employing damping techniques which damp involuntary user motion.
Hand control systems are employed in a wide range of applications, for example, in controlling air and land vehicles and in remote control applications. These hand control systems can be responsive not only to desired hand motions, but also to random hand motions due to pathological tremors, vibrations and other motions induced by the user's environment, such as air turbulence or rough terrain. Generally, the random hand motions become superimposed upon intended voluntary hand motion and, consequently, these unintended hand motions become translated into undesired system motion. Suppression of these random and induced hand motions would reduce deviations between the desired and actual system performance.
In the context of aeronautics, both helicopters and airplanes are increasingly controlled by "fly-by-wire" techniques wherein there is no direct mechanical linkage between the pilot/operator and the vehicle control surfaces The side-arm control sticks being developed for fly-by-wire helicopters typically incorporate four degrees of freedom. Since airframe vibration is a serious concern in helicopter design, damping is desirable in sidearm controllers to prevent potentially unstable growth of vibrations coupled through the pilot's arm and the control stick.
Prior approaches to this problem have relied primarily on electronic damping techniques. Circuits which damp electronic control signals are disclosed, for example, in U.S. Pat. Nos. 3,989,208 and 3,901,466 issued to Lambregts; and in U.S. Pat. No. 4,094,479 issued to Kennedy, Jr. Unfortunately, such approaches add complexity to the signal processing of "fly-by-wire" systems.
A hybrid electromechanical damping system is disclosed in U.S. Pat. No. 4,477,043 issued to Repperger. In this patent, an aircraft control stick having two degrees of freedom is equipped with variable tension springs and dampers which can be adjusted to resist undesirable forces. A processor-based system senses forces exerted on the aircraft (e.g., by acceleration) and generates a signal for causing the control stick to resist such forces. Another active force feedback system for aircraft is disclosed in U.S. Pat. No. 4,236,685 issued to Kissel. However these types of "active control" are also quite complicated in application.
A mechanical damping system for an aircraft side-arm controller is disclosed in U.S. Pat. No. 4,069,720 issued to Thor. In this system, a two-axis side controller is equipped with two discrete rotational dashpots to damp vibrations. However, this system is rather cumbersome and requires adjustments so that the controller is properly positioned vis-a-vis the physiological center of rotation of the pilot's hand in each instance. Additionally, both Thor's system and that disclosed in the Repperger patent inherently have preferred directions, i.e. directions in which rotation occurs about only one of the axes. This effect is particularly pronounced when movement of the hand control is in a direction only slightly different from one of the preferred directions; in such instances, the slip-and-stick sensations of overcoming Coulomb friction can leave the operator with a feeling of unevenness in use.
There exists a need for better hand control systems that can provide better and simpler damping mechanisms. Moreover, there exists a need for hand controls that have more than two degrees of freedom and employ damping techniques without directional preferences to suppress unwanted user hand motions. Furthermore, there exists a need for better manual controls for helicopters and other aircraft, which controls are relatively insensitive to induced hand motions, for example, from airframe vibration or turbulent air.